Resolve merge conflicts between feature and root branches

[Copilot]

PR #12 had merge conflicts with the root branch due to divergent PubSub implementations. The feature branch introduced an agnostic PubSub interface supporting both In-Memory and GCP backends, while root had a pattern-based implementation.

Resolution Strategy

• README.md: Preserved agnostic PubSub documentation (In-Memory & GCP), batch operations, and metrics sections. Incorporated improved documentation structure from root (Contributing, Acknowledgments, Support sections)
• go.mod/go.sum: Kept feature branch versions (Go 1.24.0 + GCP PubSub dependencies)
• main.go: Retained agnostic PubSub demonstration code
• memorystore/memorystore.go, memorystore/pubsub.go: Preserved PubSubClient interface and implementations

The merged codebase maintains the advanced feature set while improving documentation completeness.

// Agnostic interface preserved
type PubSubClient interface {
    Subscribe(topic string) (<-chan []byte, error)
    Publish(topic string, message []byte) error
    Unsubscribe(topic string) error
    Close() error
}

// Auto-selects implementation based on config
config := Config{GCPProjectID: "my-project"} // Uses GCP
store := NewMemoryStoreWithConfig(config)

// Or environment variable
// GOOGLE_CLOUD_PROJECT=my-project -> GCP PubSub
// (unset) -> In-Memory PubSub

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